Lenny Abrahamson’s “Room” is a true two-hander. Based on Emma Donoghue’s best-selling book of the same name, the film stars rising starlet Brie Larson and newcomer Jacob Tremblay as a mother and son trapped in extraordinary circumstances — in a single room. In the drama, Ma (Larson) has been trapped in a room (really a retrofitted woodshed) for seven years, a horrific captive situation that has only been brightened by the birth of her now-five-year-old son Jack (Tremblay). The film follows the pair as they attempt to carve out a normal existence in Room, as they call it, only punctuated by emotional upheavals and the occasional appearance of their captor, Old Nick (Sean Bridgers). The film finds the pair at a critical juncture, with Ma finally pushed to find a solution to free both herself and her precious son.Larson has already garnered attention and admiration from the film community for her turns in films like “Short Term 12” and “21 Jump Street” and her television work in “The United States of Tara,” along with newer roles in “Trainwreck” and “The Gambler,” but “Room” is her most buzzed-about work yet, a film (and a performance) seemingly destined to make a play during awards time.

Larson spoke to Indiewire during the film’s Toronto International Film Festival junket, and the actress got honest about the awards race, how she plans on keeping her independent spirit strong and why her relationship with Tremblay was so firmly built on a foundation of Lego.

How do you even prepare for a role and a film as demanding as this one?With this one, there’s so many components to it that you have to break it down into little pieces and learn about each piece and combine them all together in the end. The pieces for me were: What she was like? What was her life was like before then? I wrote three different diaries for her: One at 10, one at 14 and then one at 17. To get back in the mindset, it was really fun actually, going back and remembering what it’s like to be back in those days.

Was that your idea?

It was my idea. I asked the production designer to just buy me a bunch of journals. And then every day after work I would go home [and work on it]. I would buy all these fashion magazines and did collages and talked about body image issues. And I was able to really get into that.

And then the other piece is being kidnapped, being trapped in that space for 7 years, which is very different than if you had been just kidnapped. A lot of things happen to the mind where we shut down certain awarenesses so that we can survive, so that our brain isn’t constantly going, “Get out get out get out!” You’re just calm and relaxed and accept your environment. I spoke with a trauma counselor about that and he was able to, in a scientific way, which was so interesting, explain to me where the mind would be at and how it would compartmentalize everything like that. I was also able to speak with him about the sexual trauma that was happening and how the body reacts to that, and the shield that gets put up.

And then there’s no sunlight around, so I had to speak to the doctor about what happens to the skin and what happens to the mind when there’s a lack of vitamin D. And what happens when there’s a lack of nutrition. They’re basically eating frozen vegetables, toast and maybe eventually they’ll get some cheese, maybe occasionally they’ll get grapes.

But a lot of cereal.

A lot of cereal, yes. Just not a lot of nutrition happening, so what would then happen and how the body would adapt to that, what would her body look like. Then I worked with a nutritionist myself and got on this very simple strict diet. I was doing blood tests every week, so I was totally safe and fine, but it was just getting down to the bare minimum. There were very few things that I could eat at varying moments in time. And then I was working with a trainer every other day in order to get wiry, slim down and gain muscle. I’ve never had muscle in my life.

Your body does look very different in the film.

The difference is that…my weight is the same, technically I lost 13 pounds of fat, but I gained 15 pounds of muscle, so my body looks the same, but the difference was I had muscle from doing track and doing push-ups in Room all the time and constantly carrying Jack. He is a five-year-old boy who has a ton of energy, constantly needs to be wrestled with and moved around, and I wanted to be able to feel that. Not only could I be physical with him, but that I could protect myself and him if that man came in and did some funny business.

Jacob is just heartbreaking in this. How did you two bond? This seems like something that goes beyond the standard “Oh, we had dinner together.”

Well, first it started with a very easy pizza lunch, but it wasn’t just me and him. We didn’t do just one on one at first, because we wanted him to feel comfortable. So his mom was there, the producers were there, Lenny was there and we had this very easy lunch where we were sort of introducing each other. All of us as adults knew what was happening while he was just unaware of what was going on. But he had these little Star Wars Lego people, and I started asking him some questions about Star Wars and once he realized that I knew as much as he did about Star Wars, then we had a common interest and that was the first step. And then once he found out that I knew all the names of the Ninja Turtles and that I knew which color they were and which weapons they had, and I played video games, and all of those little things became, “Oh, okay, I can talk with this person.” We found common interests to talk about.

After that first lunch, he invited me to come over that night and play Lego with him, which I’ve never felt so happy to be accepted by any person in my life as I was by him in that invitation. So I went to his apartment and played Lego, and it’s very much like that scene at the end of the movie where I apologize to him, just simple and quiet, and we were just playing and building this Ninja Turtle Lego set. Every so often he would just ask a question because he wanted to know things about me, but the questions that he asked were, “What’s your favorite color? What’s your favorite animal? What’s your favorite ‘Star Wars’ movie?”

Once we were able to get through that, after we were done playing Lego for that night he was like, “You should come over tomorrow.” I was like, “Okay,” trying to be casual about it, but I walked skipping down the hallway feeling, I hope he liked me, and then laughing to myself realizing there was no way he was thinking the same thing, that he left and was like, I want some Sour Patch Kids. There’s no way that when I left he was like, hmmm, I hope I didn’t embarrass myself back there with Brie.

That was the beginning of it. And then we spent so much time together, we had three months of rehearsal, so we spent all day together every day, and he’s just my absolute pal. He’s my best friend. I’ve never worked closer with anybody as I’ve worked with him, and I care so much about him, and it was such an absolute pleasure working with him every day, and it makes me so happy to do all this press with him.

Is he doing well with the press? Do you think he’s having fun?

Yeah, I had a conversation with him about it the other day because we call each other co-workers, because he got confused as to what we were to one another. Because it’s a very odd relationship, so it’s our pet name for one another is “co-worker.” I had asked him about it the other day because, when we go to these press events, people come up to me and they always go, “Is that little boy here?” And I noticed that I was saying, “Oh, yeah, he’s right over there!” And then they’d go over and talk with him.

Most of the time he’s good, but because I’ve spent so much time with him and I sort of have my own little piece of motherly love and intuition for him, I went, “Oh, god, I don’t want to keep subjecting him to that if he doesn’t want it,” so I had to sit down with him. I was like, “Dude, I know there’s a lot of people who want to talk with you right now, a lot of people that when they come up to me they want to talk to you, we should get a codeword maybe, we want to come up with something funny that you can say if you don’t want to talk to people right now.” And he went: “Nah!” Just like the movie. I was like, “Alright, I’m just saying it’s going to be a long road, and I don’t want to make you cranky, I don’t like it when you’re cranky, it’s no fun for anyone when you’re cranky, so if there’s anything I can do to help let me know.” He’s like, “No, I like talking with people, the only time it gets hard is when it’s past my bedtime.” I was like, “Copy that.”

His bedtime is at 8, so to anyone reading this who meets Jacob after 8 o’clock just be aware, it’s past his bedtime, he might not be so into it. [Laughs]

Like you told Jacob, this is a long road. You took the movie to Telluride before this, now you’re at Toronto, everyone is expecting an awards push. Are you looking forward to that, are you afraid of that, are you trying not to think about that and just focuse on the work?

I don’t know, I’m not afraid of it because…what is it really to be afraid of? It’ll happen or it won’t happen. The thing that would have been scary is if I went on set to make “Room” and I didn’t do a good job, so in my mind I’m like, I already did my thing.

I’m mostly just enjoying this incredible opportunity to be here when the movie is playing. It’s a disjointed art form, because it’s a very small intimate thing that we do and then it goes out all over the world and then a lot of times I don’t know, I’m not in the theatre, I can’t see what happens. So the part that I love about it at this point, at film festivals like this, is that I get to be there on the receiving end to see people, to talk with people, to have a conversation about it, and this movie in particular is doing something very special where it’s opening people up.

It’s healing people in some ways, it’s reminding them of who they are. I’ve had so many people come up to me and tell me about stories from their childhood, things from their life that it reminded them of, things they forgot that this movie reminded them of, and that’s what I think good art does, and I’m so pleased by that and to be a participant in that.

The awards stuff is just a byproduct, it’s something that happens and I’m so grateful to be part of that conversation because there’s no higher achievement in this profession than that, but I also understand that I’m 25, how much pressure can I really put on myself with that? I think the thing I can just take from this is that I’m doing good work and people are responding well to it, and that is what really matters to me.

I hope that you feel this way too, but I feel like people really root for you.

I was feeling it yesterday. I keep hearing: “I’m rooting for you.” And I’ve been laughing about it because it’s like I’m a horse in an actual race. I just was in Hawaii and when you cheer for the dolphins they go faster next to the boat, and I feel like that in this funny way, but I really appreciate that. I really love the fact that it’s not just people saying, “Oh, I loved the performance.” People are like, “You’re a kind person, we hope that good things happen for you.”

You’ve got “Kong: Skull Island” coming up, which is directed by Jordan Vogt-Roberts, who also comes from a strong indie background. Have you bonded over that?

Oh, totally. It’s a cool thing, it’s like this weird world, this new world, because independent film wasn’t such a little community as it is now. That’s a new thing, and there is this sense of independent directors that I’ve been meeting, because I’m still considered an independent actor, that we get that we came from the same thing and we all have this same sense of awe and excitement to now have the opportunity to take the knowledge that we have and the know-how, and the love of film, the love of mythology, the love of all of that real stuff.

To get the opportunity to put it on the bigger screen, Jordan and I had an extensive conversation about this when we first met, because both of us sort of rejected bigger movies for a long time. Those are never good, they never say anything good. And then when both of us, for him it was “Kings of Summer,” for me it was “Short term 12,” and we both saw the power of what a movie can do and then there was some interest in bigger movies and both of us were like, “Wait a second, what if I could still say the same honesty, the same good truth, I could still put the things that made ‘Short Term 12’ or ‘Kings of Summer’ powerful, but I could put it in a movie that’s seen by more people, why would I say no to that?” So I think as long as we keep that sort of innocence in tact, it just couldn’t be better.

You’ve also got “Free Fire” with Ben Wheatley coming up, another director who comes from the indie space. Did you go to the [“High-Rise”] premiere?

I was there! It all moved so fast and, at one point, I really needed to pee and I was sitting next to Tom Hiddleston’s assistant. He’s already seen the movie, so I kept going, “Is now going to be a good time for me to go to the bathroom?” He’s like, “No.” Ten minutes later I was like, “Is now?” He’s like, “No.” I’m like, “Ss there ever going to be a good time?” He’s like, “No, there’s no good time.” There was so much in that movie, so many amazing things happened, so many beautiful set pieces and it went in so many different directions that I did not want to leave my seat.